<html>
<head>
    <meta charset="UTF-8">    
    <title>javaScript</title>
</head>
<body>
    <h1>Demo</h1>
    <P id="content-wrapper">你是谁？</P>
    <input id="name-input" type="text" >
    <button id="send-btn">发送</button>
    <script>
       console.log(document.getElementById("content-wrapper").innerHTML);
       document.getElementById("send-btn").onclick=function(){
        document.getElementById("content-wrapper").innerHTML='你好'+document.getElementById("name-input").value
        document.getElementById("name-input").setAttribute("placeholder","caixukun");
        document.getElementById().remove
       }
    
    </script>
   
</body>
</html>